How much water does your roof put next to your wall?
This is usually the largest single water source acting on a foundation, and the cheapest one to redirect. The number surprises people.
The arithmetic, so you can check it
One inch of rain on one square foot is 0.623 US gallons. So roof footprint × inches of rain × 0.623 gives total gallons, and dividing by the number of downspouts gives what each one delivers. Nothing here is controversial — it is just arithmetic almost nobody does before spending $15,000 on interior drainage.
What good discharge looks like
- Ten feet from the wall as a minimum, further on clay.
- Downhill from the point of discharge, not into a flat spot that becomes a pond.
- Not into a neighbour’s yard, which is a legal problem in most states, and not into a sanitary sewer, which is illegal in most municipalities and can back sewage into your own basement.
- If buried: rigid smooth-wall pipe with a cleanout, not corrugated flexible pipe, which silts up and cannot be cleared.
- Freeze path considered, in every state we cover except the southern edge.
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